7 Stripe Webhook Edge Cases That Break Billing (And How to Handle Them)

Introduction Stripe webhooks power the async side of most billing systems — subscription renewals, payment failures, refunds. But they come with edge cases that aren't obvious until something breaks in production. This article covers 7 edge cases I've encountered building BillingWatch , an open-source Stripe anomaly detector for FastAPI apps. Each one silently corrupts billing if you're not handling it. Edge Case 1: Duplicate Events Stripe guarantees at-least-once delivery, not exactly-once. The same event can arrive multiple times — especially during retries. Fix: Idempotency check using event ID before processing: def handle_webhook ( event : dict , db : Session ): event_id = event [ " id " ] if db . query ( ProcessedEvent ). filter_by ( stripe_event_id = event_id ). first (): return { " status " : " duplicate_skipped " } process_event ( event , db ) db . add ( ProcessedEvent ( stripe_event_id = event_id , processed_at = datetime . utcnow ())) db . commit () Edge Case 2: Out-of-Order